Letter Re: Grey Water for Toilets


I have an idea to provide rain water for toilets when other water is not available. My thought is to place a small broad flatish tank (10 gallons or so) on the rafters in the attic above the bathroom. Then I would modify the vent through the roof to feed the tank and to still provide venting. When the tank is full, the rain would just flow over the “roof drain”. A sort of V shaped channel dam on the roof could divert additional water to the drain into the tank.

There are many possible ways to fill the toilet, ranging from a spicket just over the toilet tank to a dual valve arrangement keeping the water systems separated. Periodically the tank could be drained into the toilet to refresh the water in the tank. If the topic is interesting, I would like to know what the rest of the community thinks. – M.M.

HJL’s Comment: I doubt such an arrangement would make it past the building inspectors approval, but here are some of my thoughts:

  1. The rafters are generally not designed to carry concentrated weight unless purposely built. This limits the size of tank you can use.
  2. I have seen toilets that flush with only 1 liter of water, but I’ve never seen one that I liked. The 2.5 liter flushes start getting more to my liking. This means that a 10-gallon tank will give you, at most, 15 flushes. Is that enough?
  3. Plumbing designed to manage both systems will require backflow preventers and increase the cost.